1. Field of the Invention
The present invention relates to oxygen electrodes for alkaline galvanic cells or batteries. The electrodes comprise a catalyst-containing carbon layer, a current collector, and separating means, especially in the form of a foil, for separating a liquid chamber from a gas chamber in such a way that the gas can pass via the carbon layer to the liquid, but the liquid cannot enter the gas chamber. The present invention also relates to a method of producing such oxygen electrodes.
2. Description of Prior Art
A multi-layer, gas diffusion electrode of this general type is known from German Patent No. 19 04 608. The objective of this patent is to improve the sealing capactiy of an electrode having very high porosity without significantly increasing the resistance to diffusion; the patent proposes the placement of a water-repellent layer of powdery carbon, powdery nickel oxide, or powdery aluminum oxide and a bonding material onto the gas side. A layer of powdery fluorohydrocarbon resin is disposed on this layer, and a further water-repellent layer is disposed on the resin layer. The resin layer and the water-repellent layer are used to assure that the electrodes are sealed or watertight.
Drawbacks to this heretofore known multi-layer, gas diffusion electrode are the complicated manufacture and the power characteristic, especially with respect to the current density which can be achieved. The basis or reason for this disadvantageous characteristic is that the sintered and porous metallic member which serves as the current collector has a very complicated construction with an internally located screen of nickel. Pursuant to the disclosed embodiment, the sintered member comprises 8 g activated carbon, to which 92 g nickel carbonyl is added; the mixture is sintered. The screen of nickel is centrally disposed in the sintered member. The sintered member is provided with a quantity of a catalyst mixture of platinum and palladium, and is finally impregnated with an emulsion of polytetrafluoroethylene (PTFE) in order to make the sintered member watertight. Already this abbreviated description should make clear the complicated manufacture which has to be carried out. Beyond that, there also has been observed that for the operation of such an electrode, high power cannot be achieved with a sintered metallic layer. Thus, at satisfactory electrical outputs, the current density is 100 mA/cm.sup.2.
An object of the present invention, on the other hand, with an overall simple construction of the oxygen electrode as a multi-layer, gas diffusion electrode is to achieve a power characteristic which makes possible the achievement of the following values: during air operation, independent of the temperature, 350 mA/cm.sup.2, and during oxygen operation, independent of the temperature, greater than 1 A/cm.sup.2 ("independent of the temperature" in this case denotes a temperature range from approximately 20.degree. to 80.degree. C.). There is particularly desired that the potential of the oxygen electrode be essentially maintained even under load for a long period of time.